Planck Pre-Launch Status Papers - APC - Université Paris Diderot ...

J. A. Tauber et al.: Planck pre-launch status: The optical systemFig. 12. The figures show cuts in the radiation pattern at 100 GHz (left)and320GHz(right) intheelevationdirectionthroughthebeampeak;thehorizontal axis is in degrees, the peak of the main beam is at 85 ◦ .TheverticalaxisisindBfrompeak(whichis61.5dBiat100GHzand68.4dBiat 320 GHz). The measured level is shown in red, the initial model in blue, and the improved model in black. The regions labelled 1 and 2 showthe SR spillover (see Fig. 5). Region 1 shows an area where PO corrections are required to the GTD model. The area labelled 3 shows a regionwhere there is poor correlation between the model and the measurement; this lack of correlation could be caused by dust on the reflectors (notethat the nominal limit of the measurement noise is well below the measured level for both frequencies). The regions 4 and 5 correspond to artificialpeaks produced by known artifacts created by features of the CATR reflectors (edge serrations, milling channels). Note that the main lobe is notwell represented by this (multi-GTD) model which is specifically designed for the full sphere.Fig. 13. The RFQM radiation patterns, as measured (left) andpredicted(right). Clockwise from top left: 30,70,320and100GHz.Thecolourscales are in dB from peak. The coordinate system is as in Fig. 5. Themeasurementssuffer from some systematic effects very close to the mainbeam. Residual artifacts are also visible in the far side lobes, e.g. horizontal features at 320 GHz.7. Flight performance predictions and associateduncertainties7.1. MethodologyThe knowledge gathered on the groundwasdistilledintoapredictionof the optical performance in orbit. This prediction consistsof GRASP calculations using the inputs (i.e. PO parametersand GTD ray families) correlated with the RFQM measurements(see Sect. 5), and the most accurate estimates of the geometry ofthe telescope in operational conditions. The most interesting aspectof this exercise is perhaps the estimation of the uncertaintiesassociated with the prediction. To identify the uncertainty rangein the estimation of radiation patterns in the far field, three differentgeometries were defined:– a“nominalcase”,whichcorrespondstothemostaccurate(“best estimate”) of the as-built telescope and reflectors inoperating conditions (as described in Sect. 5);Page 13 of 22